JERUSALEM—The commander of the Free Syrian Army (FSA), the most moderate of the opposition groups fighting the regime of President Bashar al-Assad, was among the wounded and ill Syrians treated in Israeli medical facilities since the civil war began, according to an Israeli security expert.

Ehud Ya’ari and Michael Morell, at an event for the Washington Institute for Near East Policy, said that Col. Abdullah al-Bashir, who was appointed commander of the FSA in February, was among 800 Syrians who have been treated inside Israel. He did not spell out what al-Bashir was treated for but wrote that his presence inside Israel indicated a significant measure of coordination between Israel and some of the rebel militias. “Israel is extending significant amounts of humanitarian aid and perhaps other type of aid,” he wrote.

Ya’ari, who is a commentator for Israeli television’s Channel Two, said there is a sharp debate within the Israeli defense establishment and the government over how much Israel should intervene in the Syrian fighting in order to prevent radical, al Qaeda-affiliated militias from installing themselves adjacent to Israel’s border on the Golan Heights.

Although Israeli troops on the border have fired back occasionally when shells hit inside Israeli territory, the army has refrained from taking an active role in the skirmish between the Syrian army and rebel groups, which can easily be seen from the high ground on the Israeli side of the border.

An FSA spokesman told the Times of Israel in a telephone interview this week that the group was in danger of losing control of the important southern province of Daraa, where the rebellion broke out three years ago, to the Islamist al Nusra Front, a group classified as a terrorist organization by the United States. The spokesman, who identified himself as Abu Omar al-Hourani, said that al Nusra had a well-stocked arsenal. “They receive huge external support but we haven’t managed to figure out from where.” He said that the medical treatment received in Israel by Syrian wounded had caused the people of the province to regard it as “a friendly country” despite the past wars between Syria and Israel.

Meanwhile, Israel has stepped up defensive preparations in the border area, creating a new territorial division for the Golan and allocating special intelligence equipment.

Faced for the first time with al Qaeda-affiliated militias on its borders, Israel is weighing an increase in the aid it is extending to moderate Arab forces confronting the radicals.